Sticking flushing switch. Unable to disengage switch from housing. Made to work by pushing switch with screwdriver through slot. How can a permanent cure be affected ?
Sounds like a part of the mechanism has broken or come loose. Your best bet is to contact a thetford service centre. find one at: http://www.thetford-europe.com
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix camping equipment.