Yes, peat can and should be washed. Independent studies by several growers using TDS meters to analyze water taken from rinsed peat have demonstrated readings of over 1000 PPM in some cases. CP generally prefer less than 100 PPM.
This incicates a high mineral presence in peat, right from the bale. The same problem exists in silica sand: micronutrients are present in both.
There is peat, and there is peat. Natural anaerobic bacteria in the lower levels of a peat bog are responsible for adding carbonates (lime) into the peat. The best peat comes from the upper layers of a harvested bog. Lower down you start running into problems.
If these nutrients are allowed to remain in the substrate, they can favor the growth of cyanobacteria (already present as spores in the peat). These organisms have the capability of fixing atmospheric nitrogen into the mix, another no no when it comes to CP culture. This in turn provides what is needed for mosses to colonize the pot to the detriment of the plants.
So my advice is to always rinse the peat and sand that you use.
Here is my method. Take (2) 5 gallon buckets. Add peat and pure water to the first. Knead the water into the peat, and allow to stand for a few days. Then scoop out the sodden peat, and wring it out. Put this moss into the other bucket. When this bucket is half full, repeat the process. Do the same with the silica sand, rinsing it until the water runs clear.
Make up your pots with these products. I try to make up as many pots in the spring as I think I am going to need for the season. Once the pots are made up, I place them outside where the seasons rains can leach through the pots, carrying away addidtional minerals that may be present. I use the oldest pots first.
That's the way I do it.