From Malaysia, travelling by train is more comfortable than express buses. I used to travel by train back to Thailand few times. It took almost 13-14 hours depending on how long the train stops at each station. Normally, the Malaysian train (KTMB) operating from the main hub in Kuala Lumpur Sentral until their last station on the Malaysian side of Padang Besar. For travellers who travel to Hatyai, they might need to wait for the Thai locomotive to bring the coaches and continue until Hatyai. From Hatyai, travellers will need to change train if they continue their journey to Bangkok.
Lower Sleeping Booth
Ticket can be purchased at the Kuala Lumpur Sentral Station. To Hatyai, it costs around 570++Baht for lower sleeping booth which has more space and is more comfortable. The price for the upper booth is just 50 or 60Baht cheaper. The sitting coach ticket is cheaper.
Padang Besar Station(including Malaysian Immigration and Thai Immigration as well)
At the Padang Besar Station, all passengers need to get down with their luggages as KTMB will only let the Thai locomotive which is operate by (SRT) to bring 1 sitting coach and 1 sleeping coach. Malaysian border police will get on the train to make sure that all passengers get down. For those who will continue their journey to Hatyai, they need to go through the Malaysian Immigration checkpoint and then walk to the other side for the Thai Immigration Checkpoint. Both located in the same building. The border towns too share the same name. Padang Besar.
While waiting for the train to come back, I normally go to the toilet to brush my teeth and wash my face. After about 30 minutes, all passengers are allow to get back on the train. This time, Thai railway police will be joining from Padang Besar to Hatyai. There are some touts who will go along and ask travellers with backpack if they need a taxi or van to Krabi or Phuket. Each time I travel by train, I will come across the same Muslim lady which I assume to be a Thai who works for KTMB as a cleaner on the train. She has a side job which is an illegal money changer. She gives better rate than license money changer.
Tuk Tuk in Hatyai
Once the train reaches Hatyai Junction, there are more touts coming over and ask if you need a tuk tuk truck. They are cheap and just bargain with them if they offer you more than 100Baht to your destination as the price should not be more than that. The train station is in the city itself and just few blocks away from Lee Garden which is the city center. I sometimes walk there. I only take the tuk tuk truck if I am going to the bus terminal as it is quite far by foot.