Whoa...
First off, most people rinse sand religiously but other than Jim, I've not heard of anyone rinsing peat. A bucket works for the sand. Dump it in, add water, swish it around, and repeat until the water is running clear.
You have a pond? Please tell me more about your set up and how it is that the sphagnum is creating coffee stained water. You might have the pond and the bog too close and runoff is getting into the pond or you connected them. True sphagnum peat bogs and ponds do not mix in my opinion. When they are connected, it is virtually impossible stabilizing your water and clarity will be an ongoing issue unless you do repeated 50% water changes. Even with repeated water changes, you will have some of the wildest KH and pH fluctuations you have ever seen which is not good for fish or herps. If that pond is in sun, you will most probably have problems with string algae capable of out competing any Utrics and/or other aquatic or marginal vegetation you may have growing in the pond.
There are people out there who tried these types of setups and ended up removing all of their medium and replacing it with pea gravel to create their interpretation of a pond veggie filter. There are problems with this type of a set up also so most folk ultimately end up removing the pea gravel and increasing the size of their pond or removing all of the pea gravel twice a year and cleaning it before putting it all back. Please tell me what you have living/growing in that pond as well as what type of mechanical and bio filtration you are using? If the truth be known, I don't know of any filtration that exists out there capable of encouraging a suitable habitat for nitrifying bacteria that is vital to pond health for a set up where a sphagnum peat bog and pond are connected.
I have 6 ponds here on my property. Two naturally occuring and 4 that were created by me as well as a few small water features. I also have one small kiddie pool in ground bog, 5 even smaller in ground accent type bogs, and I am in the process of creating a large 2500 gallon plus in ground bog if I can ever get the excavators back over here to finish up such a small job. I'm not exactly high on their priority list at this time of year with construction full swing and the weather this past spring did not cooperate to the extent that heavy equipment could have been driven over the lawn. I have tried the bog/pond set up before. I tried it after somebody told me it wasn't a good idea. I can be very stubborn at times and figured there had to exist filtration capable of enabling me to have a combo. Arrogantly and with credit card in hand I tried to find that filtration. I now own every type of filtration known to mankind. Nothing worked save repeated water changes and constant fiddling with chemicals to adjust the KH and pH which killed off my fish and cost me all of my odonata eggs and larva as well as my herp tads. After all was said and done, I was beside myself with grief over having lost every living creature in the pond and finally contacted a friend who is a PhD in chemistry to bail me out. We separated the bog from the pond.