Standard discharge size is 1.5" hose...that's the size that will fit the barb on the deck
pumpout fitting and also the size of the inlet fitting on a macerator pump...and the size of both the inlet and outlet on most manual diaphragm
So you'll need a piece of pipe that has a 1.5" OD (OUTER diameter), which will prob'ly mean it'll have a 1.25" ID (INNER diameter). Best to take a piece of hose with you to buy the pipe to be sure. The pipe should touch the bottom, cut at about a 25 degree angle. That will leave only a little more than 1/2 in the tank.
Btw...SeaLand/Dometic also makes a kit for this, but I can't see spending upwards of $25 USD inlcuding shipping
for something you can easily make for <$10.
No need to worry about whether the pumpout can "suck up the 'chunks'"...there won't be any. Solid waste is at least 75% water
...gets broken up by the toilet pump...so dissolves in water very quickly.
You MAY be required to use a macerator pump to dump the tank. I say "may" because I know that Queensland marine
sanitation regs require that waste from a vessel within 1 mile of shore be macerated, but not sure where else in OZ that may be true.