Hi Richard, I did have an Avondale Dart 510, and the toilet cassette filler was just below the toilet window. I used to connect up the water system, then unscrew the shower head off the shower hose. Open the toilet window, and point the shower hose end into the cassette filler and turn on the shower tap until the cassette flush was full. Turnoff shower tap, bring hose back in and reconnect shower head, and replace in shower holder, Close toilet window and job done. Refill cold water barrel if necessary