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Read Instructions Thoroughly Before Use

SPECIFICATIONS

- 1500 Watts,120 Volts

CAUTION

(1 ) Have a qualified electrician install a properly grounded receptacle 
outlet, acceptable for outdoor use and protected from snow and rain, 
immediately adjacent to the location where the heater will be used, (2) 
route the supply cord and locate the heater so as to be protected from 
damage by livestock, (3) do not use extension cords, (4) inspect cord 
before using, (5) unplug heater at receptacle outlet when not in use or 
before removing from tank, (6) store heater indoors after winter season, 
(7) heating element MUST be completely submerged while in use to 
prevent risk of fire hazard, (8) do not tether unit and (9) Caution: to ensure 
continued protection against electric shock hazard, connect to properly 
grounded outlets only.

MAINTENANCE

Do not allow lime or other impurities in the water to build up on the 
heating element. The frequency of cleaning depends directly upon the 
composition of your water supply. To remove buildup, soak the heating 
element in vinegar or a lime removing cleaner obtained at any farm or  
hardware store. Then use a rough brush to scrub the element. Do not 
use steel wool or something that will scratch the element. Inspect the 
element for any cracks before reinstalling. 

GROUND FAULT INTERRUPTER 

Must be installed in the circuit. This is a very sensitive device that cuts off 
the electrical current if there is any leakage of electricity in your water 
tank. This device may be obtained from any electrician or hardware store.

WARRANTY

This de-icer is warranted 12 months from the date of purchase. If you 

believe your de-icer is defective and still within the warranty period, 

return it to the factory for inspection and possible replacement. The 

warranty is voided if (1) the ground terminal on plug has been removed, 

(2) excessive deposits have been allowed to accumulate on the heating 

element, (3) there is evidence of general abuse such as animals chewing 

on the cord. This warranty does not cover incidental or consequential 

damage resulting from either a defect in parts, materials, or operation 

failure. Some states do not allow the exclusion or limitation of the 

above damages so the above limitation may not apply to you. No agent, 

employee, or representative of  Miller Manufacturing has any authority to 

bind Miller Manufacturing to any affirmation, representation or warranty 

directed towards any products bearing the Miller Manufacturing name, 

except as stated herein. This warranty gives you specific legal rights. You 
may also have other rights which vary from state to state.

INSTALLATION INSTRUCTIONS

1. Unscrew and remove the drain plug from the drainhole of your stock 

tank. Save this plug because you will need to reinsert the drain plug 

once the heating season is over and you have removed your de-icer 

from the tank.

2. Remove the plastic nut from the de-icer.

3.

 For use in a Rubbermaid tank: 

We recommend that you remove the entire drain assembly. To remove 

this assembly you must first remove the plastic nut found on the 

outside of your Rubbermaid tank. This nut holds the drain assembly in 

place. After the nut is removed, the drain assembly can be removed. 

You should remove the threaded drain assembly, plastic nut and rubber 

gasket. Save these items to be reinstalled in your tank after the heating 

season. If you’re using a Rubbermaid tank and have removed the drain 

assembly as described above, you should choose side “B” of the nut 

as shown in figure 1. You will install your de-icer with this side facing 

the tank.

For all other tanks: 

You will note that the nut has two sides. One side is marked side “A” 

and the other is marked side ”B”. You must determine which side of the 

nut to place against the drain hole.

1. Determine the correct side by placing the nut against the drain hole on 

the outside of the tank.Try to fit the diameter of the raised inner ring 

of each side of the nut into the inner diameter of the drain hole (see 

figure 1). Choose the side that fits most snugly. This will help secure 

and center the de-icer within the opening of larger drain holes found 
on some tanks.

2. If the raised inner ring (on both sides of the nut) shown in figure 1 is 

larger in diameter than the drain hole diameter found on your tank, 
then you may use either side of this nut. This indicates that the drain 
hole is small enough to allow your de-icer to remain centered within 
the drain opening.

3. If the nut is “bumping” into the ground or any other surface which the 

tank rests on, you must shim under the tank to raise this area. The nut 
should then twist freely.

4. Be sure to leave the rubber gasket on the threaded side of the de-icer 

and against the plastic plate of the heater housing.

5. Set the de-icer on the inside of the tank. Let it rest on the bottom of 

the tank. The rubber gasket should be between the inside of the tank 
surface and the plastic plate of the heater housing (see figure 2).

6. Insert the power cord plug through the drain hole from the inside of 

the tank. When using the 99DP, depending on the diameter of the tank 
drain hole, you may have to separate the cord (see figure 3) and then 
reassemble it after it has passed through the drain hole. Be sure to 
align the arrows located on the outer diameter of the male and female 
plugs before reassembly.

7. For installation through a wide range of drain holes, the power cord of 

the 99DP can be disconnected as shown in figure 3. Note that there 
is a rubber sleeve which protects this connection from moisture. This 
sleeve should fit tightly over this connection.

This connection is 

water resistant, NOT water-proof.

 This connection should never be 

placed directly in water as electrical shock will occur! This could result 
in death or injury.

8. Test to be sure that the plastic plate and rubber gasket both fit flush 

against the diameter of the drain hole from the inside of the tank.

a) If the bottom of the 

plastic plate is bumping 
into the bottom of 
the tank surface and 
preventing the de-icer 
from laying flush against 
the drain hole-snap the 
plastic strip off along 
the groove as shown 
in figure 4. If breaking 
this strip was necessary 
then you must also 
take a knife and cut the 
overlapping piece of gasket.

9. Insert the plastic nut onto the cord using the “slot” in the nut. The 

plastic nut should be inserted so the side chosen in step #1 is facing 
toward the tank surface. If you have not completed step #1, you must 
do so before attempting this step.

10. Tighten the nut onto the threaded stem of the heater housing and up 

against the outside tank surface. Position the nut so that the raised 
ring fully inserts into the drain hole of the tank (see figure 2 and 5). 
This is only necessary if you have determined that this ring is of smaller 
diameter than the drain opening in your tank as tested by completing 
step #2. This will stabilize the de-icer.

11. Tighten this nut ‘’snug” but do not over tighten. Be sure the unit is 

unable to twist in the tank. 

If you are experiencing leaks:

a) Check to be sure the unit is fitting flush against the diameter of the 

drain plug on the inside of the tank. See step #8.

b) Did you choose the correct size of nut? See step #1.

DRAIN PLUG DE-ICERS

Item # 99DP

304053

1

1

/

2

2”

FIGURE 1

Raised 

inner

ring

Raised 

inner

ring

FIGURE 2

 

Plastic 

plate

Rubber 

gasket

Tank

surface

Plastic

nut

FIGURE 4

UP

FIGURE 3

Miller Manufacturing, Glencoe, MN 55336 USA  •  www.miller-mfg.com

INSTRUCTIONS FOR THE 

LOCKNDRY® CORDSET

FEATURES

- Plugs into any normal 3-prong outlet
- Mates with LOCKNDRY® plugs to form a water-resistant seal
- Keeps connection from separating during use
- Second, locking nut for secure connections

INSTRUCTIONS

(1) Insert the plug into the 
receptacle just as you would a 
normal extension cord making 
sure the plug is fully inserted.

(2) Slide the large nut forward to 
engage the threads on the plug.

(3) Rotate the nut to tighten the 
plug against the receptacle. 

(4) Slide the second, thinner, red nut 
forward to engage the threads.

(5) Rotate the red nut snugly 
against the larger nut.

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