Learn Russian: Механик часто лазит по трубам в подвале. - The mechanic often crawls through pipes in the basement.

The adverb часто (often) tells us this is a repeated, habitual action. For regular trips or general movement without a single specific destination, we use the multidirectional verb лазить rather than the unidirectional лезти.

Is it 'crawls' or 'climbs'? How do I know how to translate лазит?

The verb лазить covers both climbing (using hands and feet, like on a ladder) and squeezing through or crawling inside tight spaces. The context of moving по трубам (through pipes) tells us 'crawls' makes the most sense here.

Why does 'through pipes' translate to по трубам (Dative) rather than using через?

The preposition через usually implies entering one side and coming out the other. Here, по + Dative is used because the mechanic is moving around along the length of the pipes or within the pipe network itself, which pairs perfectly with a multidirectional verb.

I sometimes see лазает instead of лазит. Are they the same?

Yes, they mean the exact same thing. Russian actually has two multidirectional infinitives for this action: лазить (which conjugates to лазит) and лазать (which conjugates to лазает). Both are correct, though лазить is often preferred in everyday speech.