1. When a non-corrupt political party comes into existence with a chance of winning.
In order to get a chance of winning, a party needs traction. In order to get traction, it needs a non-trivial amount of votes. If you refuse to vote for a party that "does not have a chance of winning", you deny them the opportunity of getting that chance.
2. When those who commit serious crimes in official capacities are charged, prosecuted, and jailed for them.
3. When those who fund the politicians are charged, prosecuted, and jailed for their serious crimes.
For #2 and #3 to become reality, you need to take care of #1 first.
I have hopes, but I have to get back to improving porcine aerodynamics first.
How about spending your time helping the non-corrupt get more influence? The next generation will appreciate it.