Ok, I donít know your specific rig, but Iím betting that you are misinterpreting what your tank & drains are.
The drains you see are most probably your hot & cold water low-point drains, which are used when winterizing your rig to ensure no water remains in the water supply lines. Ergo, you will not get much water drainage from those lines, especially if no water pressure is present.
Your hot water tank drain is normally located right on the water heater itself, accessed from behind a panel on the side of the rig.
You other tanks are as follows:
- fresh water tank
- black sewage water tank
- grey sewage water tank
All of these tank drains should be labeled somewhere on the rigÖ either in the wet bay (if your rig has one), or by cable-pull handles on the underside of the rig.
The fresh water tank (or cold water, as you think of it) will probably drain direct to the groundÖ while the 2 sewer tanks (black & grey) will drain via your sewer outlet.
As you say you are new to camping, may I respectfully suggest you read at least one of these books, and research some new camper videos on YouTube. They will explain a lot: