Concerning steps 1 & 2 of Mojojojo's method.
You should always add the acid or alkali to water, never the other way round. It gives off massive heat and could (in very extreme cases) explode.
I recommend that you add the caustic soda to a container of water. Add some,and stir it until it's dissolved. Add more...etc etc...until it won't hold any more in suspension.
Fix the pipe in a secure position and slowly pour in the juice. Probably best not to hold a hot pipe that's fully of stuff that dissolves skin and bone.
Then generally follow the rest of the steps.
Sorry but I had to jump in because this is a case of been there and done that.
Case 1: About 15 years ago cleaning out the goo from a Chappy (or a Chally, can't remember) pipe. Got the caustic soda mixed up OK, but then it became too hot to handle. I dropped it, and was lucky that it didn't get me, but it was a narrow squeak as it splashed out. The 50cc slowped ran like a dream when it was all clean and free flowing though.
Case 2: About 30 years ago I was in my mate's laundry at the pub where he lived. We were knocking up something to dissolve coke cans (I've no idea why!....because we could I suppose). In went the powder, in went the water, it boiled over, we ran for cover knocking over a kerosene burner in our haste and set fire to the guest room sheets
His old man rushed in to put it out and then gave us both a proper hiding 