The answer is vacuum. Diesel engines don't produce their own vacuum unlike gasoline engines. Diesel engines do have a vacuum pump to aid power brake boosters and help with air conditioning, automatic hubs etc..
Businesses that clean portable toilets use the power of vacuum to suck number 1,2 and that blue concoction out of the sani-pot, Honey bucket, Skookum what have you.
Their design is cheap and easy. Hardly any moving parts.
There are several spots to T into the vehicles vacuum system underneath the hood. The goldenrod fuel filter housings w/ racquetballs inside keep vegetable oil from getting sucked into your pump.
Parts List For Cummins with Hydro boost brakes:
1/4" DOT approved air brake line x 20'
1/4" Compression fitting to 1/8" FNPT
3/4"FNPT x 1/8" FNPT bushing
3/4"FNPT x 1" MNPT Reducer x3
1" Ball valve x3
1" MNPT Close x3
1"MNPT x 2"
Golden Rod Filter housing x2
Raquetball x2
1" 90 degree elbow
55 gallon sealed barrel
2" MNPT Bung bushing to 1"
1" MNPT 90 degree to 1" FNPT
1" Fuel Hose
3ft of pipe that ties into a ball valve at the end of the hose
Made sure to use Teflon tape where any plastic threads where due to the nasty effect that pipe dope has on plastic.
