Is it a rule not to dump your tanks when selling?

bandit86 wrote:
Rock solid extra extra fibre brown dirt. Went to flying J to empty and almost nothing came out.

In another discussion I mentioned this new product from Walex called Commando Black Tank Cleaner which might be worth a try. This isn't a tank treatment you'd use on a regular basis but a tank maintenance product you'd use just a couple of times a year.