Guess that would be specific to the operator.

So far we have had one coach excursion (no toilets on board) and everything else has been on minibuses (ditto) - they have made toilet stops however.

Depends where you are travelling to - Hurghada -Luxor for example we had a loo break as the convoy assembled in Safaga (the worse loos I have been to ANYWHERE in the world - and I have been to a fair few places!!!) and one stop at the "services" between Safaga and Luxor. As far as I recall there was only the one service station through the desert section of that route to stop at anyway.................

BTW it's always a good idea to carry paper hankies with you in Egypt in lieu of loo paper - and antibacterial handwash is a MUST.