A couple more thoughts on this subject...
I've posted on this forum about being turned away from campgrounds with our boat. The reason (if one is given) is that the owner has had to deal with effluents being dumped on the ground... that's not poopy water, that's ANY liquid. Many campgrounds have rules about "non-standard camping units" (anyone remember when we put up a tent so we could stay... even though we didn't stay IN the tent?).
Some campgrounds do not allow pop-up campers for the same reason: many do not have a gray tank to contain their wash water. Common strategy for that is to run a hose out to a 5 gallon bucket (like Boris mentions) to contain the water.
Think this doesn't affect local/state laws? The state of Arizona has a ridiculous law that states: your sewer HOSE may not touch the ground. That's right, not only what's coming out of it, but the actual HOSE itself! We were in AZ during most of March and had to make sure our HOSE was contained in some fashion so it didn't touch the ground. This is at ALL campgrounds in the state. We went to Home Depot and bought some plastic rain gutter to keep the hose from touching the ground.
The Wal-Mart in Rapid City wanted to build a new Super Wal-Mart a few years ago. It was delayed for over a year because local residents were up in arms about people staying in RVs in the lot and "dumping their waste tanks." I never saw this, can't imagine anyone would ever dump a black tank, but it cost Wal-Mart thousands of dollars to defend this and in the end they had to expand their proposed parking lot by over 20% and agree that the lot would be patrolled.
The new Wal-Mart in Spearfish has "NO OVERNIGHT PARKING OR CAMPING" signs all over their lot. If you park there overnight, you will be visited by the local police and told to move. The old Wal-Mart there allowed overnight parking, but too many people took advantage by staying multiple nights.
There is a book published, and even the Wal-Mart atlas that tells which Wal-Marts that no longer allow overnight parking. Please read the following link:
http://www.walmartatlas.com/no-park-walmarts
Wal-Mart, Camping World, Flying-J, Cabela's, Bass Pro/Outdoor World... it would be a darn shame to have these convenient overnight parking places completely disappear because of the actions of a few. Education and respect will go a long ways towards keeping these available.
Respectfully,
Jim B.