I learned this trick from a marine air conditioner service, in cleaning the condenser of a marine AC unit, which is a heat exchanger of sorts for the feron.
I prep two 5 gallon buckets....one with water, and the other with a 50/50 mixture of water and muriatic acid. Next, I have a small rule bilge pump, wired to two alligator clips with a 10 foot wire, for positive and negative. Hooked to the bilge pump is a hose of the right ID that will fit the pump and the inlet to the first main heat exchanger from the raw water pump. This hose is long enough to get from there back to the bilge pump which is in the bottom of the acid bucket. (You will not hurt the bilge pump) My 135's have 3 heat exchangers in series, the main heat exchanger, the oil cooler, and the transmission cooler. (removing the hose from the RW pump to the heat exchanger..to be replaced back when finished)
Then remove the hose from the exit of the transmission cooler (the hose that puts water in the exhaust mixing manifold) and connect another hose..long enough to get back to the acid bucket. You now have a closed loop system to pump the acid mixture through all the heat exchangers. Pump for a few minutes, and notice the instant color change in the acid water. After a few minutes, disconnect the power from the BP and move the pump and discharge hose to the fresh water bucket, and turn it on again, to flush the acid. Walla...clean heat exchangers.
Foot note...remove all zincs BEFORE acid flush..replace removed zincs with temporary plugs that fit. Replace with new zincs.
I find that this process is much, much less work, easier, then physically removing heat exchangers from the engines...after the proper hoses are reinstalled, start the engine to further flush for a few minutes and to check for leaks..