I have a water tank on my roof (not attice due to flat conversion years ago). I recently had my flat roof re-felted and the tank lid replaced. I think some gunge got into the tank while the work was going on as my hot water has been not running as hard since. The heat is fine - it just doesn't ran as hard. I had this problem before in another flat and someone had to come and flush my pipes out and clean the tank. Is there an easy method to do this myself (I am not too hot at DIY)? Thanks