In this paper, we consider a tabletop molecular communication (MC) system for exchange of information through flow assisted diffusion of ethanol chemical molecules. Designing modulation and demodulation algorithms for such setup is an important research problem. We propose a demodulation algorithm using Sampling based Adaptive Threshold Variation (S-ATV) for Pulse Position Modulation (PPM) and ON/OFF keying (OOK) based modulation techniques. The performance of BER with bit duration is plotted for proposed demodulation algorithm as well as Increase detection algorithm (IDA). It is found that the proposed S-ATV demodulation algorithm has better performance than IDA for smaller bit durations. © 2018 IEEE.