The drains for the shower, toilet and sink all connect to a common line. Assuming the toilet is not backing up, the problem indicates that there may be a partial blockage, enough so that some of the toilet flow is backing up through the shower drain line. You need plumbing repair. The shower leak you mention should only be in the shower, or else you have a broken drain line as well.
Grey is usually dirty water but not toilet water (shower, sink drain) Black (or Brown) is sewage from the toilet. If you have a motorhome there will be two sewage tanks... "grey" and "black"
you pee in the shower?
Sink is not vented properly and the water from the p-trap under the sink COULD be sucked out by the hydrostatic pressure from the toilet flushing.
yes, by eating it
This indicates that it has a toilet, sink and a shower but no bathtub. A 1.50 indicates that it has a toilet, sink but no shower or bathtub.
A bathroom would have a toilet-sink-tub and or shower. A half bath has a toilet maybe a sink but no tub or shower.
sink,toilet, and bathtub/shower
no
A 3/4 bathroom means that it has a shower, but not a bathtub. 1/2 bath - Toilet (and maybe a hand sink) 3/4 bath - Toilet, hand sink, shower Full bath - Toilet, Sink and bathtub
A half-bath consists of a sink and toilet. A full-bath consists of a sink, toilet, bath and shower and a three-quarter bath consists of a sink, toilet, and stand-up shower.
If it has a toilet, sink, and shower, it is a 3/4 bath. If it has a toilet and sink, it is a half bath. If it has only a toilet, it is a latrine.
rest room: toilet and a sink bathroom: toilet, sink and a shower or a bathing tub sometimes both
The minimum size of a toilet room can vary depending on what's included in the room. It may only contain a toilet, a toilet and sink, or a toilet, sink, and shower or tub or both.
it has a toilet, sink, shower and tub. (if it has a shower stall and no tub it is called a 3 piece)
Bath, toilet, sink, shower, mirror, toothbrush, shaver ?
usally a line stoppage