Emptying it so often is probably doing more harm than good. Septic tanks rely on naturally occurring bacteria to help break the waste down. Keep the use of detergents, (especially bleach), to a minimum, no fat to be put down sinks etc, and the 3 P's, (Pee, Poo and Paper) only down the W.C.'s.
If the tank is fitted with the correct lid, and ventilation system (if any), then it shouldn't smell in normal operation, although this hot weather may not help matters. Before you part with 10K on something you may not even need, I'd get the current set up checked out. Just remember, every drop of water going to that tank, needs to get away again via the soakaway. If the soakaway is waterlogged, and the tank backing up, then you will have problems, however that requires a new soakaway, NOT a new tank.