bowgurl1980

Oh, what a relief! Thank you for responding so quickly. I'll let her know.

normally there's no passport control around schengen countries by land

Hi, there is no border control between Luxembourg and Belgium.  It is part of the Schengen Area - International travelers are controlled when they first arrive in the area, but usually not between countries (exceptionally, controls happen, but currently nothing listed between Luxembourg and Belgium).   Your sister should not encounter any problems in her short trip to Belgium.  Wishing her the best of luck. 

I just read that PCG site again and it says, Dual Citizens irrespective of which passport used for travel have to pay travel tax if the stay is for over 1 year. But it also specifically says if your arrival stamp is on a Philippine passport, you get exempted from travel tax. Doesn't say anything about not needing to get the waiver if you're using a foreign passport. The TIEZA page also has inconsistencies:

Balikbayans whose stay is less than 1 year, and then on the right (requirements column), duration of which is at least 1 year. Like... which is it? 
 
I would just get the waiver which any of them will be happy to take and get on with my life, rather than open myself to the possibility of another nonsensical argument about useless red tape and bureaucracy at the airport.
 

So if you look at the TIEZA page about the Travel Tax exemption,  you will read that the 2nd to the last box in the table in the 'WHO MAY BE EXEMPTED FROM PAYING THE TRAVEL TAX' section applies to you, a dual citizen. So like with all of the others types of exemptions, these people who are exempted have to get a Travel Tax Waiver if you don't want to pay travel tax. 
 
If you look at the Philippine Consulate page about Dual Citizens, there's a FAQ section that says exactly what you have to do: get a Travel Tax Waiver.

 
If you don't get a Waiver, the person at the check in counter for your airline will ask you to pay the Travel Tax. You will tell them that you're exempted. And then they'll tell you to walk yourself to the TIEZA counter so you can get a Travel Tax Waiver and come back to them so they can give you your boarding pass. It's also possible that you've already paid the travel tax as part of your ticket, (some airlines automatically charge for this when you pay for the ticket exiting Philippines), you're good to go. I don't think they do refunds.
 
If you want to try, you're supposed to be able to get the waiver online from this TIEZA page. I've never tried this though, let us know if you do!

Yep, it's the TIEZA travel tax exemption. I applied for it before going to the airport last year for my flight PH-US. I'm a PH passport holder with a GC.

Are you Filipino?   The travel tax waiver applies to Filipino citizens who are permanent residents overseas or are duel citizens.  They would need the travel tax waiver to avoid paying travel tax when departing on a Philippine passport.

Thank you. I didn't have any issue when I went to Dubai and Hongkong when I was single in 2000's. I actually didn't know about offloading that time. I just heard about it recently in social media and went into panic mode because we invested so much for this upcoming trip. Thank you for responding.

As mentioned above, PH immigration officers often target travelers who fit the profile of potential human trafficking victims. Single, young Filipinas without much of a travel history, without personal assets of their own, without a decent stable job... you know the type. 
 
I personally travelled a lot as a single Filipina and never got offloaded. I never had to show documentation about my job or assets, but I always had them with me, just in case. It helped a lot that I always answered questions confidently and in a relaxed manner. 

You're thinking about this too much and you should relax. This 'offloading' issue usually targets single female Ph passport holders that are travelling alone, don't have much travel history and look nervous. From what you've said, you're married, traveling with kids, travelling outside of PH with your husband and have a US passport aside from a Ph passport. You'll be fine. And even if you were the targeted demographic, as long as you have all the required paperwork for your kind of travel, can converse firmly, truthfully and with confidence, you'll also be fine. Just arrive with enough time for Immigration BS when departing Philippines (at least 3 hours).
 
Since your Ph stay is less than 1 year (at least when you go to Bali), don't forget to get the travel tax waiver at the airport when you leave the Philippines.

Driving in Manila is like swimming with sharks.

I applied (and approved) for my Dual Citizenship in November last year at Phil Embassy in DC and the document was notarized before I went there.