Instructables

How to drain an RV's black and gray tanks.

Step 5: If you have a portable waste tank.

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 If you have a portable waste tank like we do currently, then there are some extra steps.

This step is more of an overview of how we do it rather than a "how to"

Our tank drains from the broad face rather than the thinner bottom, this in combination with where we have access to drain it forced us to create a way to elevate the tank. 

To elevate the tank we installed a pulley system which uses a metal ring at the bottom of the storage building, a pulley at the top and a cable puller and some rope to connect it all together.

These tanks are very heavy when full, I weight about 280 lbs. (127 kg) and with my entire weight on the other side of the pulley we could barely get the tank moving, so I would guess that the tank completely filled would weigh at least my weight. The point of mentioning this is ---SAFETY---, use only rings, pulleys, ropes and pullers rated for for the appropriate weight, everything in our system is rated for 400 lbs. (181 kg)

We have extended a pipe from the sanitary sewer to just outside the house. 

First with the tank still flat on the ground I remove the large cap from the tank and the sewer line from the house and attach the sewer hose to both,

I then lift the tank vertical and attach it to the rope (leaving the smaller breather cap on until after it is vertical and attached) then I remove the smaller cap so that the vacuum from the move starts a syphon and begins to drain the tank.

As the tank drains I lift it with the cable puller until it's as high as it will go, I drain until empty, and then lift and drain the excess in the hose.

After the tank is empty I attach the hose to the breather port and rinse the tank well before storing.



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