towing travel trailer with full holding tanks?

My general rule is to dump as soon as I can. We had one incident a few years ago where we camped at a lake high in the mountains with no dump sites. Although not totally full, when coming off the mountain we were at an angle where the grey tank backed up into the shower and overflowed onto the floor. As far as dumping, most rv parks will let you dump for a fee. In Oregon many state parks will let you dump for free. Some states still have free dump sites at road side rest areas.