One thing I learned through experience is that if you attach a rope to pull the diffuser up to clean, the rope needs to be attached in such a way so that the diffuser will pull up out of the water right side up and go back in correctly also.
Some of my diffusers use a factory Matala plastic base which I filled with gravel for weight. Problem was, they make no provision for attaching a rope to the diffuser base nor did the double diffuser base seem sturdy enough to just run a rope around the middle of it. Matala uses two single diffuser bases attached together in the middle by a couple of straps to make a double. It is actually a very nice base and is plenty well built for holding the diffuser, but it is just not made to be pulled up by rope.
So, being the handy guy that I am, I made a base out of 2x4's that was a little wider (to sit wider and have more support on the bottom of the pond). Then to this wood frame I attached via 2 points a rope that was tied above the diffusers into a knot where the rope went to the surface as a single rope with a small 4" float attached.
The problem was, after adding the boards and attaching the rope to the boards, the unit was top heavy. So while trying to lower it into the pond from the boat it wanted to tip upside down. I then re-designed so the center of gravity would be higher and solved the problem. The last picture in the attachments did not work as pictured. I ended up drilling holes in very close to the diffuser base then it worked, but a couple of "eye" bolts 6" long through the boards so the rope attachment would provide a higher center of gravity would be even better and may get modified if I pull them again. I usually just scuba dive to clean the diffusers off though, so they may never get pulled back up again till the diffuser itself actually fails.
On the next diffusers I used in my smaller pond, I just made the base myself out of quickcrete and solved all of the above problems. There are probably some plastic bases that are made to be pulled up by rope, but at least mine were not so I had to improvise.
Here are the home made versions.
home made diffuser base making the diffuser base Not a very wide base so maybe not suitable for sitting on sediment laden pond bottoms without something bigger for it to set on.
Here is a thread that shows a dirty diffuser.
cleaning diffusers 
