[Mike Haven]

here's one way of working it out from first principles:

you have seen 5 cards

3 are your suit

there are 47 unseen cards, including 10 of your suit

so the turn will be your suit 10 times in every 47 turn deals

for ease of the next stage of calculations, multiply these figures by 46

so the turn will be your suit 460 times in every 2162 turn deals

and of these 460 successful turn deals the river will also be your suit 9 times in every 46 river deals, for similar reasons as above

or 90 times in the 460

so that means that both will be your suit 90 times in 2162 turn plus river deals

or once in every 24

so the odds against receiving a runner runner flush are 23 to 1