Gray water Transfer Pump
Ever notice how the Gray water tank fills up in a hurry when dry camping, but the Black water tank never gets very full? I plumbed in a water pump to move gray water from the gray water tank to the black water tank. I used a standard RV Shure-flo pump with a strainer on the inlet. It picks up the gray water from about 1/2 way up the side of the gray tank, and pumps it to a fitting on the black water tank vent pipe about 1 foot above the black tank. This guarantees that black water can't be siphoned back into the gray tank. I have used this pump often since I set it up, and it works like a champ. It really extends your stay, especially if you have a city water hookup, but no sewer at the campsite.
The pump is a standard Sure-flo RV pump with a strainer on the inlet. I mounted the pump in the back of a compartment and installed a switch near the rig's monitor panel.
The pump output is routed through clear vinyl tubing to a fitting drilled and tapped into the black water tank vent. This ensures that black water cannot be back-siphoned to the pump. It is important to monitor the black water tank level when using the pump as it is possible to overfill the tank. Be careful!
The pump inlet is connected to a fitting solvent welded to the gray water tank. Most of these tanks are ABS plastic, and standard ABS fittings and glues are usually available at hardware and plumbing stores. If you can't find them locally, J.C.Whitney sells a kit of water tank fittings and glue to be used with the camper water tanks they sell and this will work just fine. The reason I placed the fitting halfway up the tank is to avoid sucking up either the scum on top of the gray water or the sludge on the bottom of the tank. This has been a great mod for me, and it allows me to extend a dry camping stay significantly.... Good luck with it!
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