Kitchen Sink Drains to Black Tank

My bathroom sink runs into the black tank. It was probably done because it was easier than running it to the grey tank. This seems to be fairly common.

In any case, I like it because the grey tank always fills faster than the black. In previous RVs we used to dump dishwater into the black tank.

This is the first I have heard of the kitchen sink being plumbed into the black tank.

Technically kitchen sink water is black water due to the food particles. But it is really unusual for it to be plumbed into the black water tank. The kitchen sink usually goes to the gray water tank or a separate galley tank.

When in ultra conservative mode we wash dishes in tubs and poor the water into the toilet to save space in the gray. We fill the gray tank probably three times to filling the black tank once in normal use.

I would think, in a two tank system, that would be ideal. Many people complain of running out of gray tank space and pouring water into the toilet to save what space they have. This lessens the problem and also helps alleviate the 'black tank pyramid.'

I have a three tank system and would love to have my kitchen sink running to my black tank and using both gray tanks for the shower/bathroom sink. I could go even longer when boondocking. After five days, my shower gray is almost full but my black and kitchen gray are about 1/3 full each.

Some makers feel that the black tank needs more water to be effective. This is their way of creating that assuming that most owners don't use enough water when they flush.

I can't tell you what it's common, but my kitchen has it's own gray tank which is great. Have you looked to see if adding a tank is possible? It not only adds capacity but when I have full hookups I leave that one open and never have to worry about it.