If it is not sticky, then you can use a garden water hose, as long as you have a better than good flow rate, fit the hose to the bottom rad hose and feed the output from the top hose into a large bucket.
Use the full flow rate but it may be easier to remove the thermostat - otherwise you have to have the engine running hot to open the 'stat... Even if you remove the 'stat then it can help to have the engine running but it won't get hot.
Also, do the same for the rad...
If it is sticky then you may consider a tank and external pump to do the same thing, oh and be VERY careful if you add a chemical to help remove the "sludge". Make sure it won't kill the seals.
Done this in the past, but not for that product.