Others have speculated about it being a refueller based upon a T-26. It's definitely a Soviet T-26 variant, not a Vickers or 7TP. It's been some time since I read the book where I saw it. It could be a fuel variant, but something niggles and it could be a chemical warfare sprayer, capable of spraying a persistent agent like Mustard Gas and doubling up as a decontamination sprayer (to neutralise Mustard Gas and the like).
Just be careful if you see the term "Chemical Tank" with regard to Soviet kit. Soviet FT tanks were regarded as part of the chemical warfare service. The term "OT" seems to have been used mainly, if not exclusively, post war. So OT-133 would be used post war for the KhT-133 where KhT means "Khimicheskiy Tank" and would have been the term pre and early war.,
Just be careful if you see the term "Chemical Tank" with regard to Soviet kit. Soviet FT tanks were regarded as part of the chemical warfare service. The term "OT" seems to have been used mainly, if not exclusively, post war. So OT-133 would be used post war for the KhT-133 where KhT means "Khimicheskiy Tank" and would have been the term pre and early war.,