Bringing a bicycle into Kenya (Nairobi)

I have an old second hand Trek bicycle that I'd like to bring with me on the plane into Kenya. I'm not sure how the tax duty would work, how will customs know the value of the bike to calculate this? I bought it for pennies and don't want to pay a huge amount in duty as the bike is worth very little money. Anyone shed some light on this?

Many thanks.

Tracey