if your intake grates are under the hull then get fake a lake water flush like what we use for the wakeboard boats.

Google fake a lake

it looks somewhat like a toilet plunger but can be adjusted in heights. We use it all time for those style of intake grates under the hull. as all the wakeboard boats commonly have this set up.

If you have transom mounted water pickups for the water intakes engine cooling side then fake a lake will not work

My formula 272 has fresh water dockside flush. Hose fittings for each engine. It tees into the sea line from the outdrive, with I assume a check valve on the sea side. I now have the same issue with trs. I take the caps off the sea strainer and put the garden hose in it, works fine for now

they are not under the hull just at the transom... like the old flatdecks foxhunter and tag and release on here..
here are some examples look at the transom photos in the centre

http://www.offshoreonly.com/classifi...o58409-en.html

http://www.offshoreonly.com/classifi...o59193-en.html

Why is my response 2 posts back?

[ATTACH=CONFIG]531765[/ATTACH]

For what it is worth here are where my fresh water flush is, and yes you need a plastic connector that goes on the end of a garden hose that is a quick disconnect into the fitting under those blue rubber caps that I circled.