Flojet 18555-000A 12V DC Portable RV Waste Water Transfer Pump with Garden Hose Adapter - Ideal for RV, Camper, Marine & Off-Grid Waste Management

I have found these pumps to be very good at pumping tanks except that they overheat because they are “Ignition Protected” spark-proof motors without any thought given on how to cool the motor so that it could run long enough to pump down 3 full RV tanks.The overheating problem is a failure mode also because the motor stops running when the over-temperature switch (inside the rotor?) pops, and the next time the switch pops sooner. I made a pump motor unusable because I innocently let the motor over-heat multiple times and pop the thermal cut-out and pretty soon the cut-out came on after 45 seconds! In order to get my tanks drained before the new motor arrived, I rigged up an Arduino as a timer to only run the pump for 30 seconds and then cool for a minuteThe original design of this macerator was probably for use on boats which require a spark-free motor to avoid bilge explosions because of potential gasoline vapors. Also, boats probably don’t have holding tanks as large as RV’s. Because the motor is totally sealed to be spark-free, there is no way for the heat to get out of the motor interior where is coming off the copper windings on the rotor. It is quite surprising that no thought was given to cooling of the motors since the rest of the design (except for the weak and brittle plastic material chosen for the pump housing) appears to be well thought out. I am currently pumping 5 gallons per minute through 125’ of 3/4” hose with a 10’ rise with no problem except for the motor overheating. For the RV application, the motors should be a fan cooled non-spark-free design, or be switched from being a brushed DC motor with spark producing brush-to-commutator interface, to a brushless DC motor (with controller) which are inherently spark-free and which have the copper windings attached to the housing where they can more efficiently give up their heat to the environment.Except for the motor overheating and brittle plastic I find this macerator well-suited to providing a complete RV waste-water solution. I have continued to use the Arduino as a controller and added a pressure switch to sense the pump running dry and a water valve to control water flow to my black tank flush line. When I’m draining my black tank, I (actually the Arduino program) open the black tank gate valve and run the pump until the pressure switch tells me it’s dry, shut off the pump (which stops the flow in and out of tank). I then have the Arduino program turn on the black tank flush valve for about 40 seconds to spray ~3 gallons of water into the tank. The program then shuts off the flush line and turns the pump on until the pressure switch signals it’s dry. I repeat this seven times and by then I can see through the clear elbow before the FloJet that it’s looking pretty clean.After draining and flushing the black tank, I close the black tank gate valve and use the program to add 2.5 gallons of water to the black tank and I add 4 oz of orange Camco TST treatment to the tank. I then pump down my two grey tanks, and flush the grey water out of the hose by manually connecting a fresh water hose to the fitting on the FloJet and running the pump. I keep one of the grey tank gate valves open while the water is flowing into the FloJet fitting so I don’t inadvertantly pressurize my sewer lines with the water coming in.The FloJet package does not provide the hose or the connection to the sewer pipe. I like being able to provide my own hoses but was surprised at how much time it took me figure out that combining a 3” hose cleanout fitting with a normal Camco 3” hose to sewer fitting one could work. I had to remove the ball valve from the cleanout because it was a restriction and tended to catch debris. I wish FloJet had just provided the garden hose to sewer solution. Also, I have had great luck in using copper quick-disconnects from “Gilmour 09QCGT 2-Piece Green Thumb Brass Quick Connector Set for Hose” which are a straight-through design whose only drawback are they are $11/set and I must have 10 sets! I have found that once I get these parts installed on a hose I then have no dripping at any of the connections. In the FloJet application I pump through 3 sets of these fittings (1- At the FloJet outlet, 2- Between the 25’ hose and the 100’ hose, 3- At the sewer connection) without adversely affecting the flow.I have had no luck in getting an answer from FloJet about the problem or from the several sellers of the FloJet.BTW- Does anyone know what the flat hard grey/black/brown pieces (about 2” x 3”) are that show up in the clear elbow and don’t go through the FloJet? They look like some kind of residue that has hardened into a plating that then flakes off the inside of the tank. I can’t even tell if they are from the black or grey tanks!Update: I have found that modifying the FloJet pump to provide adequate cooling is quite a bit easier than one would think. I removed the end cap from the motor which is held on by two long screws. The diecast Aluminum end cap holds the brushes, the wiring and the thermal overload switch. The end cap has two 0.5" diameter knockouts (with a little flat top) that can be opened up and a barbed hose fitting with 1/4" NPT thread can be threaded in without tapping (if you are careful) and a hose attached as the air inlet and the other hole left open as the exhaust. It's pretty easy to get the end cap back on because the outside race of the ball bearing is about the same diameter as the commutator so I was able to get the brushes on the bearing race and then slide the end cap back on, being careful to get the endcap alignment tab in its notch. I tested this setup with a small amount of air flow from my air compressor. I drained one of my tanks and the pump ran for 5 minutes without the housing even getting warm. I ordered a small (50mm x 50mm x15mm) 12V centrifugal blower for ~$7 which I think should provide sufficient airflow ro allow the FloJet to run continuously without overheating.